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Olea is a genus of 20 species of broadleaf evergreens from the family Oleaceae,
native to a variety of areas including the Mediterranean, African, Asia Minor and
Australia. It is now grown in a specific swath of the world of warm-temperate areas,
where winters are mild enough for their survival, but still have enough of a chill for
the fruiting, commercial aspect of the tree to pay off.
Olives have silvery green, leathery foliage, darker on top and silver beneath, that
helps prevent transpiration and retain moisture during periods of drought. While
immature trees have a smooth, silver-grey bark, olives gain a naturally gnarled and
twisted for as they mature. Blooms are white and born in clusters on second year
growth at the leaf axils. Fruit, green drupes growing in late summer and autumn,
ripen to a deep purple once cooler weather hits. Olives have a broad, spreading
habit, ranging from 25-45 feet (8-15m) tall in the landscape, though are often kept
even smaller for fruit cultivation. They are tolerant of wind, high altitudes, and a
variety of soil conditions. European olives can be found at altitudes from sea level to
over 4900 ft (1500m), with other species found at over 8000 ft (2500m).
Hardiness: Zones 8-11. Can tolerate short periods of below freezing temperatures in the landscape, but should be protected from
frost in bonsai cultivation, keeping ideally above 43F (6C), as it will retain leaves down to that temperature. It has an extensive,
spreading root system, and the fine feeder roots are particularly susceptible to prolonged freezes. Some cultivars are more frost
hardy than others, but as cultivars are occasionally mislabeled, it is best to treat an olive as tender. Very tolerant of areas of high
temperatures in the summer. Though they can be grown indoors, olives do best if kept outside in summer, and are given a
dormancy period in winter where they are kept at below 64F (17C).
Light: Full sun in summer, Olives grow well in hot, sunny locations. Partial shade can be given in winter.
Soil: Olive have a high tolerance for all soil types, though tend to do better in slightly alkaline (calciferous) soils. Consider
adding a form of lime in small amounts to the soil. Ensure good drainage and high inorganic content.
Watering: Have a tolerance for drought in the landscape. Water thoroughly, but less frequently, allowing it to stay on the drier
side, but never allow to dry out completely in pot culture. Olives have evolved to be water opportunists, meaning that when
water is available, they will take it up readily and quickly, but sustaining themselves when water is scarce. The rate an olive may
take up water when it is abundant can lead to a mistaken assumption that they constantly need high levels of water. Resist the
urge to over water your olive.
Fertilizer: Balanced feed through the growing season. Dose two or three times in autumn with a nitrogen free formula before
winter. Do not feed through winter. Olive can benefit from an application of trace elements once a year.
Pests and Diseases: Aphids, black scale and spider mites. Certain lepidopterous caterpillars. Verticillium wilt, Anthracnose and
Olive Knot (caused by the bacterium Pseudomonas savastanoi). Olive fly in Europe.
Repotting: Every two to three years as needed for younger trees, longer for more mature specimens. Cut back up to a third of
the root mass, leaving as much of the fine feeder roots as possible, while pruning heavy roots back hard.
Pruning and Styling: Pinch back new growth as needed during the growing season. Pinching back during the growing seasons
(spring or autumn) will result in backbudding all over the tree. Do not pinch back if you want to encourage back budding and
ramification however if temperatures are below 50F(10C) or above 100F(35C). Pinching between these temperatures will also
encourage smaller leaf size and shorter internodes. Remove buds growing directly up and down. New growth will be three
colours. First green, then purple, and finally tan. Green shoots will ramify less than those that are purple or tan. Young trees can
be pinched back to 1 to 3 leaves, depending on the direction of the last remaining bud(the direction the new shoot with grow)
when growth is purple or starting to turn tan. Older and more mature trees, where ramification is closer to complete, pinching
can be done when the shoots are green or almost purple.
When larger branches are cut during the growing season, it will result in coarse, vigorous, and often times congested new growth
at the site of the cut, which, if left unchecked, can cause inverse taper. Rub off unwanted buds as they grow to prevent that
problem when pruning larger branches. To avoid the problem all together, prune unwanted shoots that are not needed to thicken
an existing branch or trunk as early as possible. Also try pruning large branches (1in, or 2.5cm or more) in late autumn or winter
when growth has slowed. Olives can be unpredictable in their reaction to heavy branch pruning, and shortening of these can
sometimes cause the entire branch to dieback, new shoots emerging from the trunk.
Olive can be very brittle, and the bark and wood are easily damaged, so take care wiring, and only do so when necessary. Wire
young branches, under 3 years old with care, in late autumn or winter. Use raffia when wiring larger or older branches to avoid
damage.
Though deadwood is often seen on olive in the landscape, the wood of the olive rots easily. If there is deadwood on a collected
specimen, be sure to treat it with lime sulphur and possibly additional wood hardeners/preserver.
Propagation: Seeds: Pits from jarred olives will not germinate, the brine kills them. Seeds do not always breed true to the parent
tree, and are difficult to germinate, sometimes with as low as a 30% success rate. Soak in hot water or an alkaline solution for 24
hours before planting in early spring.
Cuttings: Take cuttings in late spring to early summer. Semi-hardwood cuttings, up to a half inch (1.75cm) in diameter and 4-6in
(10cm-15cm) long with root the most easily. Remove all leaves but 2-4 sets at the top of the cutting. Use rooting hormone to
increase chances. Greenwood cuttings are not always mature enough to root. Try using a mix of 90% sand or perlite and 10% peat
moss. Keep misted, but not soaking. Addition of bottom heat is helpful, and will increase cutting viability dramatically. Rooting
of hardwood cuttings can be done, though can take several months. Semi-hardwood cuttings can also be rooted sometimes in
straight water.
Truncheon: A truncheon method involves removing a branch, 3-4in (7.5-10cm) in diameter from a tree, cutting it into 12in (30cm)
lengths and planting it horizontally in well tilled, aerated soil. New shoots will often grow, and these can later be separated, or
used to create a joined root planting.
Other: Ovuli are swellings found on the trunks of many olives. These can be cut off and planted in early spring, and will root
easily. These structures contain both adventitious root initials and dormant buds so that new root and shoot systems can develop.
This process however is damaging to the parent tree, and will leave a large scar. Olive can also be propagated by removing
suckers in spring.
Styles and Forms: All styles except formal upright, broom and exposed root (though extensive, the root system is delicate and
can be easily damaged by this style).
Species and Cultivars: O. europaea Common olive, or European olive. Most common cultivated species.
“Arbequina” Smaller form, frost resistant.
“Little Ollie” a dwarf cultivar growing only 2-4 feet tall, with dark green leaves.
“Montra” Smaller habit, popular for bonsai.
“Mission” Cold hardy cultivar.
Supspecies Var. Africana. Glossy green leaves above, and brown underneath. Globular, pea-sized fruit. Freely self seeding and
considered invasive in some areas.
O. laurifolia Black Ironwood. South African native. Glossy green leaves grow up to 4inches (10cm) and are better suited to larger
bonsai. Heartwood is very hard, hence the common name, and is well suited to deadwood styles with the right tools. Zone 9-11
O. oleaster alternately classified as O. europaea oleaster. Wild olive with smaller leaves.
O. paniculata Australian Olive. Native to eastern Australia. Bushy tree, 50-80 ft (15-24m) tall in the landscape. Wrinkled bark,
glossy green foliage, oval fruit the ripens to a blue-black. Zones 9-12
Other Information: Olives have three stages of growth. At the earliest stage, when grown from seed, olive tend to grow only a
tap root, using most of the raw energy from this type of root system for trunk development. This stage can last up to seven years.
The second stage involves the sprouting of new roots. The crown will often be unwieldy and seem over grown, but will be in
proportion with the new roots that have grown. This stage will often be the starting point for airlayered trees. When an olive
reaches maturity, the fine, spreading feeder roots begin their growth, the trunk spreading and loosing it’s column form. It is also
the point where the previously smooth bark starts to crack and gain a more rugged appearance. The tap root from the earliest
stage will disappear eventually, naturally dying off as the larger, spreading root system of the more mature growth takes over.
native to a variety of areas including the Mediterranean, African, Asia Minor and
Australia. It is now grown in a specific swath of the world of warm-temperate areas,
where winters are mild enough for their survival, but still have enough of a chill for
the fruiting, commercial aspect of the tree to pay off.
Olives have silvery green, leathery foliage, darker on top and silver beneath, that
helps prevent transpiration and retain moisture during periods of drought. While
immature trees have a smooth, silver-grey bark, olives gain a naturally gnarled and
twisted for as they mature. Blooms are white and born in clusters on second year
growth at the leaf axils. Fruit, green drupes growing in late summer and autumn,
ripen to a deep purple once cooler weather hits. Olives have a broad, spreading
habit, ranging from 25-45 feet (8-15m) tall in the landscape, though are often kept
even smaller for fruit cultivation. They are tolerant of wind, high altitudes, and a
variety of soil conditions. European olives can be found at altitudes from sea level to
over 4900 ft (1500m), with other species found at over 8000 ft (2500m).
Hardiness: Zones 8-11. Can tolerate short periods of below freezing temperatures in the landscape, but should be protected from
frost in bonsai cultivation, keeping ideally above 43F (6C), as it will retain leaves down to that temperature. It has an extensive,
spreading root system, and the fine feeder roots are particularly susceptible to prolonged freezes. Some cultivars are more frost
hardy than others, but as cultivars are occasionally mislabeled, it is best to treat an olive as tender. Very tolerant of areas of high
temperatures in the summer. Though they can be grown indoors, olives do best if kept outside in summer, and are given a
dormancy period in winter where they are kept at below 64F (17C).
Light: Full sun in summer, Olives grow well in hot, sunny locations. Partial shade can be given in winter.
Soil: Olive have a high tolerance for all soil types, though tend to do better in slightly alkaline (calciferous) soils. Consider
adding a form of lime in small amounts to the soil. Ensure good drainage and high inorganic content.
Watering: Have a tolerance for drought in the landscape. Water thoroughly, but less frequently, allowing it to stay on the drier
side, but never allow to dry out completely in pot culture. Olives have evolved to be water opportunists, meaning that when
water is available, they will take it up readily and quickly, but sustaining themselves when water is scarce. The rate an olive may
take up water when it is abundant can lead to a mistaken assumption that they constantly need high levels of water. Resist the
urge to over water your olive.
Fertilizer: Balanced feed through the growing season. Dose two or three times in autumn with a nitrogen free formula before
winter. Do not feed through winter. Olive can benefit from an application of trace elements once a year.
Pests and Diseases: Aphids, black scale and spider mites. Certain lepidopterous caterpillars. Verticillium wilt, Anthracnose and
Olive Knot (caused by the bacterium Pseudomonas savastanoi). Olive fly in Europe.
Repotting: Every two to three years as needed for younger trees, longer for more mature specimens. Cut back up to a third of
the root mass, leaving as much of the fine feeder roots as possible, while pruning heavy roots back hard.
Pruning and Styling: Pinch back new growth as needed during the growing season. Pinching back during the growing seasons
(spring or autumn) will result in backbudding all over the tree. Do not pinch back if you want to encourage back budding and
ramification however if temperatures are below 50F(10C) or above 100F(35C). Pinching between these temperatures will also
encourage smaller leaf size and shorter internodes. Remove buds growing directly up and down. New growth will be three
colours. First green, then purple, and finally tan. Green shoots will ramify less than those that are purple or tan. Young trees can
be pinched back to 1 to 3 leaves, depending on the direction of the last remaining bud(the direction the new shoot with grow)
when growth is purple or starting to turn tan. Older and more mature trees, where ramification is closer to complete, pinching
can be done when the shoots are green or almost purple.
When larger branches are cut during the growing season, it will result in coarse, vigorous, and often times congested new growth
at the site of the cut, which, if left unchecked, can cause inverse taper. Rub off unwanted buds as they grow to prevent that
problem when pruning larger branches. To avoid the problem all together, prune unwanted shoots that are not needed to thicken
an existing branch or trunk as early as possible. Also try pruning large branches (1in, or 2.5cm or more) in late autumn or winter
when growth has slowed. Olives can be unpredictable in their reaction to heavy branch pruning, and shortening of these can
sometimes cause the entire branch to dieback, new shoots emerging from the trunk.
Olive can be very brittle, and the bark and wood are easily damaged, so take care wiring, and only do so when necessary. Wire
young branches, under 3 years old with care, in late autumn or winter. Use raffia when wiring larger or older branches to avoid
damage.
Though deadwood is often seen on olive in the landscape, the wood of the olive rots easily. If there is deadwood on a collected
specimen, be sure to treat it with lime sulphur and possibly additional wood hardeners/preserver.
Propagation: Seeds: Pits from jarred olives will not germinate, the brine kills them. Seeds do not always breed true to the parent
tree, and are difficult to germinate, sometimes with as low as a 30% success rate. Soak in hot water or an alkaline solution for 24
hours before planting in early spring.
Cuttings: Take cuttings in late spring to early summer. Semi-hardwood cuttings, up to a half inch (1.75cm) in diameter and 4-6in
(10cm-15cm) long with root the most easily. Remove all leaves but 2-4 sets at the top of the cutting. Use rooting hormone to
increase chances. Greenwood cuttings are not always mature enough to root. Try using a mix of 90% sand or perlite and 10% peat
moss. Keep misted, but not soaking. Addition of bottom heat is helpful, and will increase cutting viability dramatically. Rooting
of hardwood cuttings can be done, though can take several months. Semi-hardwood cuttings can also be rooted sometimes in
straight water.
Truncheon: A truncheon method involves removing a branch, 3-4in (7.5-10cm) in diameter from a tree, cutting it into 12in (30cm)
lengths and planting it horizontally in well tilled, aerated soil. New shoots will often grow, and these can later be separated, or
used to create a joined root planting.
Other: Ovuli are swellings found on the trunks of many olives. These can be cut off and planted in early spring, and will root
easily. These structures contain both adventitious root initials and dormant buds so that new root and shoot systems can develop.
This process however is damaging to the parent tree, and will leave a large scar. Olive can also be propagated by removing
suckers in spring.
Styles and Forms: All styles except formal upright, broom and exposed root (though extensive, the root system is delicate and
can be easily damaged by this style).
Species and Cultivars: O. europaea Common olive, or European olive. Most common cultivated species.
“Arbequina” Smaller form, frost resistant.
“Little Ollie” a dwarf cultivar growing only 2-4 feet tall, with dark green leaves.
“Montra” Smaller habit, popular for bonsai.
“Mission” Cold hardy cultivar.
Supspecies Var. Africana. Glossy green leaves above, and brown underneath. Globular, pea-sized fruit. Freely self seeding and
considered invasive in some areas.
O. laurifolia Black Ironwood. South African native. Glossy green leaves grow up to 4inches (10cm) and are better suited to larger
bonsai. Heartwood is very hard, hence the common name, and is well suited to deadwood styles with the right tools. Zone 9-11
O. oleaster alternately classified as O. europaea oleaster. Wild olive with smaller leaves.
O. paniculata Australian Olive. Native to eastern Australia. Bushy tree, 50-80 ft (15-24m) tall in the landscape. Wrinkled bark,
glossy green foliage, oval fruit the ripens to a blue-black. Zones 9-12
Other Information: Olives have three stages of growth. At the earliest stage, when grown from seed, olive tend to grow only a
tap root, using most of the raw energy from this type of root system for trunk development. This stage can last up to seven years.
The second stage involves the sprouting of new roots. The crown will often be unwieldy and seem over grown, but will be in
proportion with the new roots that have grown. This stage will often be the starting point for airlayered trees. When an olive
reaches maturity, the fine, spreading feeder roots begin their growth, the trunk spreading and loosing it’s column form. It is also
the point where the previously smooth bark starts to crack and gain a more rugged appearance. The tap root from the earliest
stage will disappear eventually, naturally dying off as the larger, spreading root system of the more mature growth takes over.
Olive (Olea)
| Ancient olive tree growing on the slopes of Comares in Spain. Photo by Peter Caulfield |
| Olive Foliage |
"O olive tree, blessed be the earth that nourishes you
and blessed be the water you drink from the clouds
and thrice blessed He who sent you
for the poor man's lamp and the saint's candle-light".
- Folk song from Crete
and blessed be the water you drink from the clouds
and thrice blessed He who sent you
for the poor man's lamp and the saint's candle-light".
- Folk song from Crete